1. Technical Field
The present invention relates to a printing technology for performing printing by discharging ink from a print head onto a print medium.
2. Related Art
In a serial inkjet printer, printing is performed by discharging ink from a plurality of nozzles and forming dots on a print medium while moving a print head comprising the nozzles in a primary scanning direction and a secondary scanning direction relative to the print medium. In such inkjet printers, positional deviation sometimes occurs in which the positions where the ink discharged from the nozzles of the print head are deposited on the print medium deviate from their target positions. For example, when the ink discharge timing of the forward and backward movement of the print head is not strictly constant, the relative positional relationship between the dot group formed by the forward movement of the print head and the dot group formed by the backward movement will have deviated from the target positions. In other cases, when ink of a certain amount or more is discharged onto the print medium, the expanding/contracting and undulating (so-called cockling) of the paper causes the distance between the print head and the print medium to differ between forward and backward movement, and as a result, the dots are formed deviated from their target positions.
When such positional deviation occurs, the edges of letters or lines sometimes blur, which is a cause of reduced print quality. Such problems are not limited to serial inkjet printers, and have been common to printing devices which output printed images formed by discharging ink with multiple different timings to form dots in a common print region of the print medium and combining these dots formed at multiple different timings with each other. For example, in line printers as well, wherein a plurality of print heads are arrayed in a zigzag formation across the entire width direction of the print medium and some adjacent print heads are made to overlap each other, the same problems have occurred because of the difference in the discharge timings of ink from the print heads arranged in a zigzag formation. See, for example, Japanese Laid-Open Patent Publication No. 2008-130003.